I have the same problem with a first generation 17" IMac G5 EMC 1989. Suddenly, over night, the USB ports do not work. The optical mouse no longer worked. The external HD which uses USB for power was disconnected by the computer. Further, the Brother MFC_7820N printerwhich has been connected to the G5 was rejected by another Mac as drawing too much power. It also failed to print when connected to a separate PC. So my IMac went down and took with it my printer. I can replace with a similar one today for $150.

I opened up the back of the IMac, which is very easy to do, and found a bulging and leaking capacitor. I was C5009, just for reference. My belief is that the sick capacitor caused the whole problem. I am using another computer, but for the fun of it, plan to replace all these capacitors on the mother board. see http://jimwarholic.com/2008/07/how-to-re...

1 Answer

IIRC the USB ports on your computer are directly connected to the logic board. If all the ports are dead you probably have a component problem on your logic board. Try cleaning the ports and using a simple USB mouse to test with after cleaning. Since this is a G5 if the cleaning doesn't work check out the capacitors on the logic board. Good luck.